Two-storey rear extensions in County Antrim

County Antrim at a glance

Nation: Northern Ireland
Price region: Northern Ireland
Postcode areas: BT
Towns covered: 15 listed below, plus surrounding villages
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary.
Site visits: Free, no obligation

What a two-storey rear extension involves

A two-storey rear extension is a new two-floor addition built onto the back of your house, usually giving a larger kitchen or living space on the ground floor and one or two bedrooms or a bathroom above. Because both floors share one set of foundations and one roof, it adds a lot of floor space for the garden it uses. In some cases it can be built under permitted development, depending on where you live.

Across County Antrim we cover Belfast (BT1), Lisburn (BT10), Newtownabbey (BT36), Castlereagh (BT4), Carrickfergus (BT38) and Ballymena (BT42), plus the smaller places around them.

Guide price in Northern Ireland

Expect a two-storey rear extension in County Antrim to land somewhere around £49,500–£66,500 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). Our Northern Ireland guide rate is £1,760–£2,380 per m², including VAT. Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	Typical project
Essential	£1,620–£2,190 per m²	£45,500–£61,000
Standard	£1,760–£2,380 per m²	£49,500–£66,500
Premium	£2,110–£2,850 per m²	£59,000–£80,000

Rules in Northern Ireland

In Northern Ireland, a two-storey rear extension can be permitted development if it goes no more than 3 m beyond the original rear wall and stays at least 7 m from the rear boundary, with conditions on height, materials and roof pitch. Upper side windows within 15 m of a neighbouring boundary must be obscure-glazed and non-opening. Otherwise a planning application costs £347 per dwelling.

Approval in Northern Ireland: Planning application for works to a house: £347. Councils aim to decide local applications within an average of 15 weeks; many take longer.

Building control: Building control approval from the local council under the Building Regulations (Northern Ireland), using the Technical Booklets.

There is no Party Wall Act in Northern Ireland. Shared walls and boundaries are a matter of title and common law, so we agree access and record conditions with neighbours before work starts.

Getting the design right

Foundations and drains

Foundations for two storeys carry more load than a single storey and may need to go deeper near trees or on clay. Rear extensions often sit near drains, so we check sewer records early, as building over or near a public sewer may need the water company's agreement.

Depth and neighbours' light

Councils check that a two-storey rear extension does not take too much light or outlook from neighbouring windows, and many use a 45-degree line drawn from the nearest habitable window. We test this at sketch stage, so the depth you are shown is one that can realistically be approved.

How we work in County Antrim

Free site visit
We visit your home in County Antrim, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering County Antrim.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.

Towns we cover in County Antrim

Two-storey rear extensions in County Antrim: questions

How much does a two-storey rear extension cost in County Antrim?

In Northern Ireland our guide is £1,760–£2,380 per m² including VAT, so about £49,500–£66,500 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.

Will a two-storey rear extension block my neighbour's light?

It can if it is too deep or too close to the boundary, which is why councils look closely at its effect on neighbouring windows and gardens. We test the design against light and outlook early, keep the first floor shorter or set in where needed, and use a hipped roof to reduce bulk on the boundary side.

Will I need planning permission in County Antrim?

County Antrim is in Northern Ireland. It may be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary.

Neighbouring areas

All extension services in County Antrim · About two-storey rear extensions